Field of the Invention
The invention relates to a flowmeter for flow measurement of a flowing medium having a measuring tube and a measuring device housing that incorporates at least the measuring tube.
Description of Related Art
Known variations of flowmeters are, for example, magnetic-inductive flowmeters, vortex flowmeters or Coriolis mass flowmeters.
The following designs relate to examples of a magnetic-inductive flowmeter. The explanations in terms of construction, however, are valid in general for flowmeters that use other measuring principles.
Magnetic-inductive flowmeters have been known extensively in the prior art for decades. As an example, reference is made here to the citation “Technische Durchflussmessung” by professor Dr.-Ing. K. W. Bonfig, 3rd Edition, Vulkan-Verlag, Essen, 2002, pages 123 to 167 and to the citation “Grundlagen Magnetisch-Induktive Durchflussmessung” by Dipl.-Ing. Friedrich Hoffmann, 3rd Edition, 2003, publication of the company KROHNE Messtechnik GmbH & Co. KG.
Depending on the design, magnetic-inductive flowmeters have a magnetic field generator for generating a magnetic field at least partially interfusing the measuring tube, at least one measuring electrode for tapping a measuring voltage induced in the flowing medium, and an evaluation unit. In some designs, in particular, there are two measuring electrodes.
The basic principle of a magnetic-inductive flowmeter for flow measurement of a flowing medium is traceable back to Michael Faraday, who proposed, in 1832, the use of the principle of electromagnetic induction for measuring the flow velocity of an electrically conductive medium.
According to Faraday's law of induction, an electric field strength is formed perpendicular to the direction of flow of the medium and perpendicular to the magnetic field in a flowing, electrically conductive medium interfused by a magnetic field. Faraday's law of induction is thus exploited in magnetic-inductive flowmeters in that a magnetic field fluctuating over time during the measurement process is usually generated by means of a magnetic field generator usually having at least one magnetic field coil, and that the magnetic field at least partially interfuses the electrically conductive medium flowing through the measuring tube. Here, the generated magnetic field has at least one component perpendicular to the longitudinal axis of the measuring tube or perpendicular to the direction of flow of the medium.
If the magnetic-inductive flowmeter has at least one magnetic field generator “for generating a magnetic field running perpendicular to the longitudinal axis of the measuring tube”, then the magnetic field preferably runs perpendicular to the longitudinal axis of the measuring tube or perpendicular to the direction of flow of the medium. However, it is sufficient when a component of the magnetic field runs perpendicular to the longitudinal axis of the measuring tube or perpendicular to the direction of flow of the medium.
It is also described above that the magnetic field generator is used for generating a preferably alternating magnetic field. This is not of importance for the teaching of the invention—in conformity with its origin, the objects forming its basis and the solutions for these objects—that this is an alternating magnetic field, even if magnetic-inductive flowmeters predominantly have magnetic field generators for generating alternating magnetic fields.
It is also described above that the magnetic-inductive flowmeter being discussed here also has at least two measuring electrodes for tapping a measuring voltage induced in a flowing medium, wherein the measuring electrodes preferably come into contact with the medium. Preferably, the virtual connection line of the two measuring electrodes runs at least essentially perpendicular to the direction of the magnetic field interfusing the measuring tube perpendicular to the longitudinal axis of the measuring tube. In particular, the measuring electrodes can be provided in such a manner that their virtual connection line actually runs—more or less—perpendicular to the direction of the magnetic field interfusing the measuring tube.
Finally, it is described above that the measuring electrodes are, in particular, such that they come into contact with the medium. Indeed, of course, the electric field strength generated by induction in the flowing, electrically conductive medium can be tapped by direct, i.e., galvanic measuring electrodes in contact with the medium as a measuring voltage. However, there are magnetic-inductive flowmeters in which the measuring voltage is not tapped by direct, i.e., non-galvanic, measuring electrodes in contact with the medium, rather the measuring voltage is capacitively determined.
From a functional standpoint of magnetic-inductive flowmeters of the type being discussed here, two functional units can be differentiated here, namely a first functional unit with the measuring tube and measuring electrodes and a second functional unit with the magnetic field generator, wherein an evaluation unit can also be part of the second functional unit.
Two different implementations of magnetic-inductive flowmeters are conceivable. Namely, there is a first implementation, in which the two functional units mentioned above, i.e., the measuring tube with the measuring electrodes and the magnetic field generator are already factory-set to function with one another, i.e., are components that are already factory-set to function with one another of a magnetic-inductive flowmeter that is functional when leaving the factory. There is also a second implementation, in which the two functional units are separate components that result in a functional magnetic-inductive flowmeter when the components are brought into function with one another.
In the following, the first implementation of a magnetic-inductive flowmeter is always described, i.e., the implementation in which the measuring tube with the measuring electrodes and the magnetic field generator have already been factory-set to function with one another, i.e., are components that are already factory-set to function with one another of a magnetic-inductive flowmeter that is functional when leaving the factory.
Magnetic-inductive flowmeters known from the prior art in German Patent DE 692 32 633 C2, German Patent Application DE 199 07 864 A1 and corresponding U.S. Pat. No. 6,453,754 B1, German Patent Application DE 100 64 738 B4 and corresponding U.S. Pat. No. 6,564,612 B2, German Patent Application DE 102 43 748 A1 and corresponding U.S. Pat. No. 6,804,613 B2, German Patent Application DE 10 2008 005 258 A1 and corresponding U.S. Pat. No. 7,971,493 B2 and German Patent Application DE 10 2011 112 703 A1 and corresponding U.S. Patent Application Publication 2012/0066301 A1 as well as European Patent Application EP 0 704 682 A1 and European Patent Application EP 0 834 057 A1 and corresponding U.S. Pat. No. 6,092,428 are referred to as examples.
The known magnetic-inductive flowmeters are often a “sturdy construction” in that the measuring tube and/or the measuring device housing consist/s of metal. As a general rule, these measuring tubes are tubes, i.e., cylindrical hollow bodies having a circular cross section. The measuring device housings are also often designed as cylindrical hollow bodies with a circular cross section or an essentially circular cross section. Further, it holds true for most known magnetic-inductive flowmeters that the measuring device housings have blind flanges and connection flanges consisting of metal on both sides. On the one hand, these blind and connection flanges, with which the two ends of the measuring tube are—directly or indirectly—connected, terminate the flowmeter, leading to the term “blind flange”. On the other hand, the blind and connection flanges are used for connection of both sides of the flowmeter to the corresponding piping flanges, thus “connection flange”.
The known magnetic-inductive flowmeters are generally produced for “industrial use”. For this reason, they need to have a “sturdy construction,” on the one hand, and on the other hand, need to satisfy considerable requirements for measuring accuracy.
For developing and producing magnetic-inductive flowmeters, economical aspects naturally need to be taken into consideration and these aspects are taken into consideration. Nevertheless, the costs for production are not the primary focus in the magnetic-inductive flowmeters belonging to the prior art.
The above designs are not to be limited to the measuring principle, rather are valid in large parts for other flowmeters.